Loop over list to assign names in R not working

Question

I have a bunch of rows I'm adding to a larger dataframe called bigger_false. I want to do this using for loops. Each row looks like this:

new_row1 <- c(402, 1, "false alarm", 0)

I want to assign each of the new rows names of columns of the larger dataframe, so I'm looping over each row in a list and assigning the same names to each.

rowlist = list(new_row1, new_row2, new_row3, new_row4, new_row5, new_row6, new_row1011, new_row1014, new_row1016, new_row1022, new_row1023, new_row2021, new_row3046)

for (item in rowlist) {
      names(item) <- c("guest_id", "sessionNum", "interactions.hitType", "n")
    }

Then I'm looping over each and adding them to the big dataframe, which already has those column names.

for (item in rowlist) {
      bigger_false <- rbind(bigger_false, item)
    }

Now, the first loop seems to work for the first row (it successfully gets assigned the names). So if I manually do

bigger_false <- rbind(bigger_false, new_row1)

I get no error. However, the rest of that first loop does not successfully assign the rest of the rows the names, so the rbind loop gives the error: "Argument 2 must have names" after the first iteration.

Why is this happening? Thanks in advance.

I don't think this is exactly a duplicate, but several SO posts like [this one](https://stackoverflow.com/q/12511648/5325862) should help with how to assign values back from within a loop. A fully [reproducible example](https://stackoverflow.com/q/5963269/5325862) would make it easier to help / point you to previous SO posts — camille, Sep 28 '20 at 15:07

Waldi · Accepted Answer · 2020-09-28T15:04:13.490

The item variable loops over rowlist but doesn' modify the content of rowlist.
Try:

new_row1 <- c(402, 1, "false alarm", 0)
new_row2 <- c(403, 2, "false alarm", 0)

rowlist = list(new_row1, new_row2)

for (item in 1:length(rowlist)) {
  names(rowlist[[item]]) <- c("guest_id", "sessionNum", "interactions.hitType", "n")
}

bigger_false <- NULL
for (item in rowlist) {
  bigger_false <- rbind( item, bigger_false)
}
bigger_false

     guest_id sessionNum interactions.hitType n  
item "403"    "2"        "false alarm"        "0"
item "402"    "1"        "false alarm"        "0"

score 0 · Answer 2 · answered Sep 28 '20 at 15:13

0

Instead of loops, you can also do:

# creates a matrix
df <- do.call(rbind, rowlist)

# create a dataframe
df <- data.frame(df)
colnames(df) <- c("guest_id", "sessionNum", "interactions.hitType", "n")

answered Sep 28 '20 at 15:13

YOLO

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Loop over list to assign names in R not working

2 Answers2